[MPlayer-users] RFC: docs update for "how to create a high quality DVD rip"

[Matthias Wieser]

Wayde Milas wrote:

> Here is the truth. 384k Ac3 5.1 is already compressed all to hell.
> Seriously. This is what happens: They take a master of say 6 channels
> (this isnt quite right because some of the channels arent full bitrate,
> but its close enough to get a good idea) of 24 bit sound. The sampling
> rate is usually 48khz. This is compared to CD which is 2 channels of 16
> bit at 44.1khz.

Here is the truth. MPEG-2  is already compressed all to hell.
Seriously. This is what happens: They take a master of say 2000x800 pixel
(this isnt quite right because I dont' know the exact resolution of the 
master, but its close enough to get a good idea) of 24 bit video. The 
sampling
rate is usually 24hz. This is compared to MPEG2 which is 720x576 at 4:2:0 
sampling.

> Ok so you got 6*24*48000 = 6912000 bits per second. Now they take this
> monster stream, and compress it down to 384k - 384*1024 = 393216. See
> the huge amount thats already thrown out?

Ok so you got 2000*800*24bit*24fps = 921 600 000 bits per second. Now they 
take this
monster stream, and compress it down to 6M  - 6*1024*1024 = 6 291 456. See
the huge amount thats already thrown out?


> Yes they do some funky acoustical modeling and phase shifting so it
> makes it really hard to detect the differences, and all the channels
> arent active all at once most times so alot of of the bits that tossed
> are not meaningless. The point here is that the 5.1 audio stream is
> already HEAVILY compressed.

[...]


Matthias